Generally, an aluminum heat exchanger having aluminum type fins brazed on aluminum type heat exchanging tubes is used widely. Furthermore, in order to increase the heat exchanging rate, heat exchanging tubes are made of an extruded flat tubed strip of aluminum type material.
In order to manufacture a heat exchanging apparatus constructed as above, for brazing fins and an extruded flat tubed strip together, a method is used that coats brazing metallic powder on the aluminum surface and uses a flux for brazing; and as examples of this brazing method, there are known, first, a method of coating the brazing metallic powder and the flux powder separately, and second, a method of mixing the brazing metallic powder and the flux powder and then coating with this mixture.
However, there is a problem with the first method of coating the brazing metallic powder and the flux powder separately in that it involves very complicated processes. Furthermore, although the second method of coating the mixtures of brazing metallic powder and the flux powder has a lesser number of steps than the first method, there is a potential problem of not having a homogenous mixture of the powders. If the mixture is inhomogeneous, there is inadequate brazing material at a portion where there is a larger amount of flux, which leads to a residual flux remaining after brazing; on the other hand, there is a local melting of a substrate by an excess of brazing material and concomitant decrease in actual brazing because of a shortage of flux at a location where there is an excess of brazing metallic powder.
Furthermore, when the particle size of the brazing metallic powder is too large, there is a local melting of a substrate because of an excess of brazing material in certain parts. On the other hand, when the particle size of either the brazing metallic powder or the flux powder or both is too fine, particles easily aggregate, inducing inhomogeneity to cause the same type of problem associated with the second method above.
Furthermore, in a case where a binder is not used, there is a problem of peeling off after drying the coat. Moreover, when a liquid of low volatility such as water as a solvent medium for the mixture is used, there arise problems such as increase in time for drying and inhomogeneity and concentration differences.
The present invention is conceived with the above problems in mind. The purpose of the present invention is to provide an aluminum brazing method and aluminum brazing material that can braze uniformly and with ease and certainty.